Method and apparatus for improving the uniformity of the basic weight of a fabric

ABSTRACT

A method and apparatus is disclosed for regulating the basis weight on the exit side of fabric heat set apparatus to improve the uniformity of the basis weight of the fabric in a mill roll or other selected fabric length. A measured exit fabric basis weight is averaged across the width of the fabric and the average final basis weight is compared with a selected target basis weight to produce a measured final basis weight error signal. The latter signal may be fed into an &#39;&#39;&#39;&#39;on time&#39;&#39;&#39;&#39; proportioning auto control which produces an on-time control signal proportioned to the measured final basis weight error signal and adjusts a motor operated potentiometer to vary a calculated percent moisture signal from an initially manually set estimated magnitude of the percent moisture in the fabric on the entrance side of the heat set apparatus. The percent moisture signal along with signals representing measured entrance basis weight, measured entrance fabric width, measured entrance speed, measured exit speed, and standard fabric width are fed as inputs into a calculated final basis weight computer, which computes a calculated or predicted final basis weight. The calculated basis weight is averaged in a profile averaging computer and compared with the selected target basis weight to produce a calculated basis weight error signal. The latter error signal is fed into a speed proportioning auto control which produces a speed on-time control signal proportional to the calculated final basis weight error signal. A speed motor operated potentiometer is adjusted in response to the speed on-time control signal to vary a overfeed speed control signal from an initially manually set signal. The overfeed speed control signal adjusts the speed of the fabric overfeed means which feeds fabric onto a tenter frame at the entrance end of a heat set oven at a speed greater than the speed of the tenter. By adjusting the speed of the overfeed means in accordance with the calculated basis weight error signal shrinkage of the fabric is regulated in order to improve the uniformity of the fabric final basis weight.

United States Patent McCall Dec. 24, 1974 Primary ExarninerEugene G.Botz Attorney, Agent, or Firm-William T. Fryer, Ill; Munson H. Lane,.lr.; C. Henry Peterson [57 ABSTRACT A'method and apparatus is disclosedfor regulating the basis weight on the exit side of fabric heat setapparatus to improve the uniformity of the basis weight of the fabric ina mill roll or other selected fabric length. A measured exit fabricbasis weight is averaged across the width of the fabric and the averagefinal basis weight is compared with a selected target basis weight toproduce a measured final basis weight error signal. The latter signalmay be fed into an on time proportioning auto control which produces anon-time control signal proportioned to the measured final basis weighterror signal and adjusts a motor operated potentiometer to vary acalculated percent moisture signal from an' initially manually setestimated magnitude of the percent moisture in the fabric on theentrance side of the heat set apparatus. The percent moisture signalalong with signals representing measured entrance basis weight, measuredentrance fabric width, measured entrance speed, measured exit speed, andstandard fabric width are fed as inputs into a calculated final basisweight computer, which computes a calculated or predicted final basisweight. The calculated basis weight is averaged in a profile averagingcomputer and compared with the selected target basis weight to produce acalculated basis weight error signal. The latter error signal is fedinto a speed proportioning auto control which produces a speed on-timecontrol signal proportional to the calculated final basis weight errorsignal. A speed motor operated potentiometer is adjusted in response tothe speed on-time control signal to vary a overfeed speed control signalfrom an initially manually set signal. The overfeed speed control signaladjusts the speed of the fabric overfeed means which feeds fabric onto atenter frame at the entrance end of a heat set oven at a speed greaterthan the speed of the tenter. By adjusting the speed of the overfeedmeans in accordance with the calculated basis weight error signalshrinkage of the fabric is regulated in order to improve the uniformityof the fabric final basis weight.

7 Claims, 2 Drawing Figures TENTER I2 '2 FRAME OVERFEED I5 ROLLER sets'R E EE" Q -r HEAT SET I2 OVEN 25 w v RIABLE 5 ,jwloTrIj E 24 PROFILE 23I E x33 AVERAGINGI COMPUTER ENABLE W? t 26 mm CONTROL 29 SUPPLY TUB FTERTIME T 27 CALCULATED MOTOROPERATED iINITIAL Z WEIGHT I% MOISTURE)'POTENTIOMETER SET IvIA SET COMPUTER BWC r30 PROILE ew AVERAGINGCOMPUTER ENABLE EACH SCAN INITIAL MOTOR OPERATED sPEEosET POTENTIOMETERMETHOD AND APPARATUS FOR IMPROVING THE UNIFORMITY OF THE BASIC WEIGHT OFA FABRIC The invention relates to a method and apparatus for improvingthe uniformity of the basis weight of a travelling web of textile fabricat the exit side of fabric heat setting apparatus.

Fabric containing synthetic resin fibers, such as the double knitpolyester fabrics, are subjected to a heat set process for the purposeof setting the fabric so that it will retain its weave. A typical heatset apparatus will include a source'of fabric supply from a prior fabrictreating station, generally where the fabric is wet with a liquidtreating media for cleaning, sizing, or other purpose, overfeed meansfor feeding the fabric onto a tenter frame which carries the fabricthrough a heat set oven and regulates the stretch and/or shrinkage ofthe fabric in one or more directions, and a fabric take up means on theexit side of the heat set oven where the fabric is wound into a largeroll known as a mill roll.

Design and economic factors enter to make it highly desirable to obtaina mill roll in which the fabric throughout its entire length and breadthis substantially of a uniform basis weight. Factors which affect thefinal basis weight of fabric on the exit side of a heat set oven are thebasis weight of the fabric entering the heat set apparatus, which inturn is affected by the moisture content of the fabric, the amount oflateral and longitudinal shrinkage, and/or stretch within the heat setoven, and the moisture content of the fabric at the exit side of theoven. Most of the factors effecting final basis weight can be measuredand controlled to some degree of accuracy, but the measurement andcontrol of all the factors affecting basis weight requires expensivemonitoring and control equipment. Since the cost of the monitoring andcontrol equipment is increased with the number of factors affectingfinal basis weight that are measured and controlled, it is highlydesirable from an economic standpoint to keep the monitoring and controlequipment to a minimum while obtaining a product of optimum basis weightuniformity which will satisfy the needs of marketplace.

One known method which has been proposed for controlling a fabric heatset apparatus includes measuring the fabric basis weight and moisturecontent ahead of the oven, before the overfeed. From these measurementsthe dry fiber weight may be calculated. The dry fiber weight is comparedwith the desired final target weight. Any difference would result in acontrol signal being applied to the overfeed means to increase ordecrease the final fabric weight to the target weight. The final fabricweight after the oven would be measured and displayed as an indicationto the operator of how well the process was being controlled to thetarget.

It is a primary object of this invention to monitor and control thefinal basis weight of a fabric at the output side of heat set apparatusin order to obtain improved uniformity of final basis weight whilekeeping the cost of the basis weight monitoring and control equipment toa minimum compatible to obtaining the desired uniformity of final basisweight. In conformity with the aforesaid primary objective of thisinvention, the monitoring and control equipment of this invention omitsapparatus for directly measuring the moisture content of the fabriceither at the entrance or exit end of the heat set apparatus.

It is an object of this invention to measure the final fabric basisweight (weight per unit area) and control the final basis weightrelative to a target basis weight by making adjustments to the speed ofthe overfeed means feeding fabric onto the tenter frame that carries thefabric through the heat set oven. For the purpose of this invention itwill be assumed that certain conditions of the heat set apparatus aresubstantially met. For one, the heat set oven is of such design that itwill dry the fabric substantially completely, secondly the tenter frameis adjusted to produce a fabric at the exit side of the heat set ovenwhich has a selected standard width, and thirdly by controlling thespeed of the overfeed means laying the fabric onto the tenter frame thelongitudinal shrinkage of the fabric can be regulated, and thus byregulating longitudinal shrinkage of the fabric, the final fabric basisweight can be controlled within acceptable limits relative to a selectedtarget.

Factors affecting the difficulty of final fabric basis weightmeasurement and control are: a long transportation lag through the heatset oven (transport lag can be one-half of the length of the productbeing run), a high moisture content in the fabric before the oven(typically thirty percent), width change in the fabric at the entranceend which affects weight per unit area, and fabric shrinkage while goingthrough the heat set oven.

The method of this invention includes measuring the fabric entranceweight, fabric width, and fabric speed at the entrance side of the heatset oven before the overfeed means, measuring the fabric final basisweight and speed at the exit side of the heat set oven, comparingthe'final basis weight with a selected target basis weightand obtainingan error signal which is used to increase or decrease the magnitude ofan initially estimated percent moisture signal in proportion to errorsignal, feeding the percent moisture signal together with known andmeasured parameters into a computer and solving the following equationfor calculated final basis weight:

where BW, is calculated final basis weight, BW is. measured entrancebasis weight, S is speed of fabric before overfeed means, S is speed offabric after oven,

W is width of fabric near BW gauge, W is standard width of fabric afteroven, and D is estimated or computer percent moisture of fabric atentrance (expressed as a decimal),

' comparing the calculated basis weight BW with the target basis weightand producing a difference calculated final basis weight error'signal,and applying the difference calculated, final basis weight error signalto increase or decrease the speed of the overfeed means in proportion tothe error signal.

The method of this invention thus provides the following importantfeatures:

I. Feedforward control with closed loop feedback as to the controlledvariable. The measurement of entrance basis weight is before the pointof control actuation, but the actuator (overfeed means) speed basisweight and which may be presented on a motor operated potentiometer dialor other display means;

3. Calculation of a predicted final fabric basis weight which iscompared with a target basis weight to produce an error signal forvarying the speed of fabric overfeed means in order to regulate fabricshrinkage and thus to regulate final fabric basis weight; and t t 4. Afurther closed loop feedback, supplying the actual exit-basis weight asmeasured by the exit basis weight gauge, as a check on the calculatedfinal basis weight. The measured final basis weight is also comparedwith the target basis weight, and any error is used to adjust theestimated moisture entry in the computer, so that an overfeed controlaction may be made which will ultimately conform the actual exit basisweight tothe target basis weight.

Importantly, this control method gives closed loop feedforward controlfrom the first fabric basis weight gauge so that control actions can 'bedone'each scan without waiting for the transportation through the oven.An assumption made here is that the unknown variable affecting finalbasis weight is predominantly moisture in the fabric at the entrancebasis weight gauge and that the feedback from an auto controllerresponsive to the difference between a measured final basis weight and atarget basis weight can be used to fine tune the control system of thisinvention to the proper value so the initial calculations are true. Ifthis is true, changing fabric weights can be easily done by the operatorsimply changing a target setting to the new weight. If the moisturepickup is the same as the old fabric, he will be on target; if not, theexit basis weight gauge will have to adjust the moisture motor operatedpotentiometer to make the calibration correct. If the moisture pickupchanges significantly from fabric to fabric and is not predictable, thenthe'm'oisture can be measured. However, moisture measurement is adifficult and costly measurement which should be avoided where possible.

The apparatus of the invention includes appropriate gauges of known typefor measuring the fabric entrance basis weight, entrance speed, entrancewidth, exit speed and fabric exit basis weight, a variable speed drivefor the fabric overfeed means, a speed motor operated potentiometer forgenerating an overfeed speed control signal and having means forinitially manually setting'the overfeed speed, a speed auto control ofknown type for producing an on-time control signal for adjusting thespeed motor operated potentiometer in direction and in proportion to acalculated final basis weight error signal, means for averaging themeasured final basis weight across the width of the fabric and comparingthe average final basis weight with a target basis weight to produce ameasured basis weight error signal, a percent moisture auto controlresponsive to the measured basis weight errorsignal to produce anon-time control signal which is proportional to the measured basisweight error signal, a percent moisture motor operated potentiometer forgenerating a percent moisture signal in response to the on-time controlsignal from the percent moisture auto control and which includes meansfor initially manually setting an estimated percent moisture signal, acomputer for calculating a predicted final basis weight according to theaforesaid calculated basis weight equation, using measured entry basisweight, entry width, entry speed, final speed, and calculated percentmoisture as variable inputs, and having means for setting in a standardfabric exit width, a profile averaging computer for averaging 5 thecalculated final basis weight across the width of the fabric and forcomparing the calculated final basis weight with the target basis weightand generating a calculated basis weight error signal which is appliedto the speed auto control to control the speed'motor operatedpotentiometer. The entrance and exit basis weight gauges are preferablyacross-fabric scanning gauges.

The auto controlfor the speed motor operated potentiometer is preferablyenabled each scan of the entrance basis weight gauge and the autocontrol for the percent moisture potentiometer is enabled aftersufficient time has elapsed to allow for the lag time between the momentwhen the overfeed means is adjusted and the moment when material at theoverfeed means at moment of adjustment reaches the exit basis weightgauge. The latter enabling control can be in response to a selectednumber of scans or number of feet of process material passing the finalbasis weight gauge. 4 The term basis weight as used herein is inaccordance with the common usage of the term in the textile industry andis the weight per unit area of textile fabric including any moisturepresent in the fabric.

With the foregoing objects and features in view and such other objectsand features which may become apparent as the specification proceeds,the invention will be understood from the following description taken inconjunction with the accompanying drawings, wherein like character orreference designate like parts and wherein:

FIG. 1 is a diagram'schematically illustrating a preferred embodiment ofthe present invention, in combination with a textile fabric heat settingfacility.

FIG. 2 is a block diagram of the measuring, computer, and controlcircuits employed in the system of FIG. 1. 1

With reference now to the drawings and specifically to FIG. 1, theinvention is diagrammatically illustrated in combination with typicalapparatus for heat setting fabrics which contain synthetic resin fibers,as for example double knit polyesterfabrics. The typical heat settingapparatus includes a material supply 11, a series of guide rollers 12, adriven overfeed roller 13, a tenter frame 14, a heat set oven 15, andfabric wind up means 16. The material supply illustrated in FIG. 1 is atub in which a batch of fabric is folded with the trailing end 10' ofthe fabric draped over the edge of the tub so that it may be sewn ontothe lead edge of another batch of fabric in another tub by a sewingmachine (not shown) typically provided at the site. The fabric 10supplied in 55 the tubs 11 is usually wet having been taken from aliquid bath in which the; ;fabric was treated for cleaning, sizing, orfor other purposes and may typically contain in the order of thirtypercent moisture. The different tubs of fabric are previously sorted sothat the basis weight of each batch of fabric connected together at theentry end of the heat setting machine does not vary extremely from aselected basis weight. Normally the wind up reel 16 will receive thecontent of a number of batches of fabric supplied atthe input end. Sinceit is desired that 'the basis weight of the material on the windup reelbe substantially uniform, the need for sorting the batches of fabric atthe entry end according-to weight arises in order that the heat settingapparatus will not require extreme adjustment with each different batchof fabric. Fabric from the tub is fed over a series of guide rollers 12at the entry end of the heat set apparatusb y a driven overfeed roller13 and is laid onto a tenter frame 14 which carries the fabric throughthe heat set oven 15 at a somewhat slower speed S than the speed S ofthe overfeed roller 13. The tenter frame 14 may be selected from varioustenter frames which are well known in the art. A typical tenter framewill include a pair of laterally spaced endless belts, or chains 14(only one shown) carrying pins 17 for gripping opposite edges of thefabric. The belts 14' extend through the oven 15 and are supported atopposite ends of their loops by pairs of sprockets 18 and 19 (only onesprocket of each pair is shown). Provision is made for adjusting thelateral spacing between the belts 14' in order to stretch and hold thefabric web to a desired and uniform width at the exit end of the heatset oven 15. In the present invention the tenter frameis adjusted forfabric of a desired width to be delivered to any given wind up roll andwill normally not be readjusted while fabric is being applied to any onewind up roll. In order to accommodate and control longitudinal shrinkagewithin the heat set oven 15 the fabric web 10 is overfed onto the tenterframe by an overfeed roller 13, the speed of which is con-trolled inaccordancewith the present invention. A rotary brush 19 at the entry endof the tenter 14.forces the lateral edges of the fabric web 10 onto thetenter pins 17 so that the fabric is wrinkled, or waved, as indicated at20 between pins as a result of excess fabric. The amount of overfeed isregulated in accordance with the present invention to control the amountof longitudinal shrinkage in order to obtain a uniform basis weight ofthe fabricat the exit end of the heat set oven. The heat set oven 15provides a controlled high temperature environment for heat setting anddrying the fabric 10 so that the fabric leaving the oven is assumed-tohave approximately zero percent moisture and the required heat setcharacteristics. The heat set process effects the elastic memoryof knitpolyester fibers or other synthetic resinous fibers in a manner wellknown in the art. The length of the oven 15 which is necessary toprovide the proper heat set characteristics and drying of the fabric 10is'normally long so that there is a long time delay before measurementsmade at the exit end of the oven, and used to adjust the overfeed rollerspeed, will be reflected in the measurements at the exit end of theoven.

It is emphasized that this invention is adaptable for use with the heatset equipment to be found in various textile plants which may vary inone or more particulars from plant to plant, the typical heat setapparatus shown in FIG. 1 being given by way of example only. While abatch type supply is illustrated it isto be understood that a continuousweb supply from a previous fabric fabricating, or other process, stepmay be provided.

The monitoring equipment of the invention includes an entry basis weightgauge 21 for measuring the basis weight, BW of the fabric being fed fromthe supply tub 11, an entry width gauge 22 for measuring the edge toedge width W an entry speed gauge 23 for measuring the speed S of thefabric being fed by the overfeed roller 13, an exit speed gauge 24 formeasuring the speed 8;, of the fabric at the exit end of the heat setoven, and an exit basis weight gauge 25 for measuring where the basisweight, BW of the fabric at the exit end of the heat set oven. The basisweight gauges 21 and 25 are preferably a cross-sheet scanning beta raygauge of well known construction. They contain well-known internalcircuitry (not shown) to render theoutput signal thereof proportional tothe weight or mass per unit area of the travelling web which includesthe weight of the moisture and the fabric fiber. Other gauges can beused to generate signals indicative of the weight per unit area.

The width gauge 22 may be any one of several well known width gauges forproducing an electrical signal proportional to the' width of the web.10. One such gauge includes a pair of edge sensors (not shown), such asphotoelectric cells, mounted on a double threaded lead screw fordetecting the opposite edges of the fabric. A servo system is providedfor rotating the lead screw to keep the photoelectric cells in positionfor developing a web edge position signal and a slave potentiometer isdriven with the lead screw to give an indication of the distance betweenthe two opposite edge detectors. One such gauge is illustrated in FIG. 1of U.S. Pat. No. 3,341,888, W. A. Bridge et al., Sept. 19, 1967.

The speed gauges 23 and 24 are preferably tachometers of the well knownvoltage generating type which are operatively connected to selectedguide. rollers 12 and are driven by the fabric moving thereover. Thespeed gauges 23 and 24 produce an output voltage which is proportionalto the fabric speed at the points of measurement.

The signals 8W W W S and BW are fed as input signals into a computer 26which solves for an estimated or calculated final weight at the exit endof the heat set oven according to the equation:

BW Calculated final fabric weight BW, Basis Weight of fabric at entryend W Width of fabric at entry end W, Selected Standard width at exitend S Speed of fabric as fed by overfeed roller S Speed of fabric atexit end of heat set oven D Calculated percent moisture in fabric atentry 7 end The standard width W,, is the width of the fabric-at theexit end of the heat set oven as it comes off the tenter frame 14 and istherefore normally constant once the tenter frame has been adjusted forthe desired final width of the fabric. W, is manually set into thecomputer by a potentiometer adjustment. The percent moisture input D isderived from a motor operated potentiometer 27. Initially D is anestimated value of the percent moisturein the fabric at the supply endof the heat set apparatus, but after the heat set apparatus beginsoperating, D, becomes a calculated value obtained by taking thedifference between a target basis weight BW, and the measured exit basisweight BW The difference between BW and BW, is assumed to result from anerror in the estimated or calculated value of D and therefore the speedof the overfeed roller S is adjusted to bring BWQ closer to BW,.

It is to be understood that the amount of longitudinal shrinkage offabric 10 may be decreased'from a predetermined maximum at some highrate of overfeed by the overfeed roller 13, by decreasing the speed ofthe overfeed roller so that less excess fabric 10 is accumulated betweenthe pins 17 on the tenter frame at the lower speeds. Since the fabrictends to become heavier as the fabric shrinks longitudinally, the basisweight BW at the exit end increases with-increased fabric shrinkage anddecreases as. the shrinkage becomes less. Thus the exit basis weight 8Wmay be increased or decreased by increasing or decreasing the speed S ofthe overfeed roller 13 within limits. The only value in the equationgiven above for calculated final fabric basis weight which is not eithermeasured or known is the percent moisture D Therefore when the measuredexit basis weight BW differs from the target basis weight BW,, it isassumed that the percent moisture input D is in error; that is, D, doesnot correspond with the actual percent moisture in the fabric on thesupply side. The difference between the measured exit basis weight BWand the target basis weight BW, is obtained from a profile averagingcomputer 28 of a type known in the art. The profile averaging'computer(PAC) 28 obtains a running or current average value BW of the exit basisweight BW of the fabric web 10 along the width thereof. instantaneousvalues of BW are fed into the PAC 28 from the scanning exit basis weightgauge 25, the integral of this parameter with respect to time iscalculated and the integral is divided by the elapsed time to obtain thedesired running average BW One profile averaging computer suitable foruse with the invention is illustrated and described in US. Pat. No.3,566,092, granted to Michael P. Grant and Henry T.

Jaggers, on Feb. 23, 1971, assigned to the same assignee as the presentinvention. A comparing circuit (not shown) is provided in the PAC 28 forobtaining a signal which is equal to the difference between the averageexit basis weight BW agdthe target basis weight BW,. This differencesignal BW BW, is fed into the auto control 29 which is a reset typecontroller of known type, incorporating means proportioning eachcorrective'adjustment to the magnitude of the error signal and providingmeans for suspending control action after each adjustment .until after apredetermined length as determined which will allow the material subjectto the corrective action of this invention to reach the measuring gauge25.

One suitable auto control 29 of a reset proportional controller type isillustrated and described in conjunction with FIG. 2 of US. Pat. No.2,895,888 granted to Donald E. Varner on July 21, 1959, assigned to theassignee of the present invention. The auto control 29 will provideeither an increase or decrease signal to a motor operated potentiometer27 depending on whether the difference BW -BW, is positive or negative.The auto control signal whether positive or negative will be on for atime proportional to the difference I between BW and BW,, and will beoff -for a time approximately equal to the time T required for materialto travel from the overfeed roller 13 to the exit basis weight gauge 25.The off time can be determined by an automatically resetting odometerengaging the fabric 10 and providing a signal indicating the passage ofa predetermined length of the traveling material, or the off time may bedetermined by an automatically resetting counter which counts the numberof scans made by the scanning gauge 25 and provides a signal after apredetermined number of scans.

The motor operated potentiometer 27, includes control means whereby itmay be initially manually adjusted to provide an initial percentmoisture D, output which is estimated by an operator. After the initialmanual setting is made the auto control 29 takes over and adjusts themotor operated potentiometer automatically to produce a correctedpercent moisture output signal. The percent moisture output signal D isfed to the calculated final basis weight computer 26 which solves thepreviously given equation for calculated basis weight BW The outputsignal BW from the computer 26 is fed to a profile averaging computer(PAC) 30 which is similar to the profile averaging computer 28. Th e PAC30 obtains a running or current average value BW, of the calculatedbasis weight across the width of the fabric 10 for each scan of theentry basis weight gauge 21. The average calculated final basis weightPW; is compared with the target basis weight BW, which is manually setinto the PAC 30 by making a potentiometer adjustment. A comparingcircuit (not shown) is provided in the PAC 30 which produces an outputsignal which is equal to the difference between the calculated averagefinal basis weight BW and the target basis weight BW,. This differencesignal BW -BW, is fed into an auto control 31 similar to the autocontrol 29 which proportions a corrective adjustment to the magnitude ofthe error signal and suspends control action after each adjustment for apredetermined time. The auto control 31 is enabled each scan of theentry basis weight gauge 21 and produces either an increase or decreasesignal output toa motor operated potentiometer 32 depending on whetherthe difference BW BW, is positive or negative. The auto control signal,whether positive or negative, will be on for a'portion of the timebetween each successive scan of the entry basis weight gauge 21 which isproportional to the difference between W and i I The motor operatedpotentiometer 32 is like the M.O.P. 27 and includes means for manuallymaking an initial potentiometer setting for establishing a predeterminedinitial speed of the overfeed roller 13. Its output is applied toa'variable speed drive 33 which varies the speed of the overfeed roller13 in accordance with the error signal from the auto control 31 once thesystem has become operative. a

FIG. 2 illustrates the components of the monitoring and control systemof this invention separated from the components of a typical fabric heatset apparatus and shows the components of the calculated final basisweight computer shown within the block 26 indicated by dash lines. Thecomputer 26 includes an adder circuit 40 which adds one plus the percentmoisture signal D derived from the M.O.P. 27, a divider circuit 34,which divides BW 'by l D a second divider circuit 38 which dividestheameasured width signal W by a standard width signal W, obtained froma manually set standard width potentiometer 39, a multiplier circuit 35which multiplies BW /l D, by W,/W,, a second multiplier circuit 36 whichmultiplies (BW /l D )'(W,/W,) by the speed signal-S derived from thesupply feed tachometer 23, and a third divider circuit 37 which divides(BW,/l D )-(W /W,)'S by the speed signal S;, taken from the exit speedtachometer 24. The adder, divider and multiplier circuits within thecalculated final weight computer 26 are selected from well knowncircuits for performing the indicated func tion, therefore furtherdescription thereof is deemed unnecessary.

While no attempt has been made to illustrate the visual signal displaysprovided in the apparatus of this invention, it will be understood thatmeans for visually displaying and/or recording the various measuredparameters, targets, constants, and calculated values may be provided asdesired. The profile averaging computers 28, and 30 used with thisinvention each have a strip chart recorder provided with an indicatorpen and pointer mechanism which register the average exit basis weightBW and the average calculated basis weight BW respectively. The profileaveraging computer recorders also include a target indicator assemblycomprising a target pointer which may be positioned relative to a scaleby means of a mechanically coupled target setting knob. The targetadjustment is used by the operator to set a desired target basis weightBW,. Whenever the indicating pointer is not in alignment with the targetpointer an error signal is transmitted to the auto control associatedwith the respective profile averaging computers 28 and 30. Meanspreferably will be provided in the profile averaging computers for selecting various scales and edgeof scale settings in a known manner foruse with the strip chart recorder. One strip. chart recorder of the typediscussed herein is illustrated and described in US. Pat. No. 2,895,888previously referred to.

The motor operated potentiometer 27 and 32 each have an indicator scaleand pointer (not shown) associated therewith for indicating thepotentiometer setting, whether manually set by'a control knob, orautomatically set by the motor operatively connected to thepotentiometer arm. The M.O.P. 27 is calibrated in units of percentmoisture, and the M.O.P. 32 is calibrated in units of speed. An operatorby observing the M.O.P. 27 is thereby able to observe the calculatedvalue of percent moisture being fed to the computer 26.

While analogue measurements have been described,

it will be understood that digital measurements, computations anddisplay by means well known in the art may be substituted within thespirit and scope of this invention. Further, conversions from analogueto digital, and from digital to analogue can be made as desired in orderto facilitate optimum efficiency and economy compatible with thestandards required for the inventron.

While in the foregoing there has been described and shown a preferredembodiment of the invention, various modifications and equivalents maybe resorted to within the spirit and scope of the invention as claimed.

What is claimed is:

1. A method of improving the uniformity of the basis weight of atravelling web of textile fabric at the exit side of fabric heat settingapparatus which includes a source of wet fabric supply, means for heatsetting the fabric, tentering means for obtaining a uniform standardwidth of the fabric at the exit side of said heat setting means and forregulating the longitudinal shrinkage of the fabric by said heat settingmeans, overfeed means for moving said fabric web from the source ofsupply onto said tentering means, means for winding up said fabric webafter it has passed through said heat setting means and means, forvarying the speed of said overfeed means, comprising the steps ofgenerating a signal BW, indicative of the measured basis weight of thefabric on the entry side of said heat setting means, generating a signalW indicative of the measured width of the fabric on the entry sideofsaid heat setting means, generating a signal S, indicative of themeasured speed of the web on the supply side of said tentering means,generating a signal 5;, indicative of the measured speed of the web onthe exit side of said heat setting means, generating a signal 8Windicative of the measured basis weight of said fabric on the exit sideof said heat setting means, generating a signal BW, indicative of apredetermined target basis weight for the web on the exit side of theheat setting means, comparing the signal BW withthe signal BW, andproducing an error signal BW BW, which corresponds with the deviation ofthe signal BW from BW,, initially setting a signal D indicative of anestimated percent moisture content of the web on the entry side of theheat setting means, and thereafter automatically increasingthe signal Dto indicate an increased percentage moisture when BW is greater than theBW, and decreasing the signal D to indicate a decreased percentagemoisture when BW is less than BW, in proportion to the magnitude ofdeviation of BW from BW,, generating a signal BW indicative of acalculated exit basis weight according to the formula:

c l W1/(l 1)]( s)'(. 1/ 3) wherein BW BW W S S and D respectivelyrepresent previous indicated signals and W represents a preset signalindicative of a selected standard width for said fabric at the exit sideof the heat setting means, comparing the signal BW with the signal BW,and generating an error signal BW -BW, which corresponds cludes a webfabric supply source, means for heat set-,

ting the fabric, tentering means for obtaining a uniform standard widthof the fabric at the exit side of said heat setting means and forregulating the longitudinal shrinkage of the fabric by said heat settingmeans, overfeed means for moving said fabric web from the source ofsupply onto said tentering means, means for winding up said fabricweb'after it has passed through said heat setting means, and variablespeed drive means for said overfeed means, comprising means forgenerating a signal BW indicative of the measured basis weight of thefabric on the entry side of said heat setting means, means forgenerating a signal W, indicative of the measured width of the fabric onthe entry side of said heat setting means, meansfor generating a signalS indicative of the measured speed'of the web on the supply.

side of said tentering means, means for generating'a signal S indicativeof the measured speed of the web on the exit side of said heat settingmeans, means for generating a signal 8W indicative of the measured basisture content of the web on the entry side of the heat setting meansincluding means for manually setting said moisture signal generatingmeans to an initial signal magnitude means responsive to the errorsignal BW -BW, for automatically increasing the signal D to indicate anincreased percent moisture when BW is greater than the BW, and fordecreasing the signal D to indicate a decreased percentage moisture whenBW is less than BW, in proportion to the magnitude of deviation of BWfrom BW,, computer means for generating a signal BW indicative of acalculated exit basis weight-according to the formula:

wherein BW BW,, W 5,, S and D respectively represent signals previouslydefined and W represents a preset signal indicative of a selectedstandard width for said fabric at the exit side of the heat settingmeans, means for comparing the signal BW with the signal BW, and forgenerating an error signal BW -BW, which corresponds with the deviationof BW from Bw means for generating a speed control signal which'controlsthe speed of said variable speed drive including means for manuallysetting an initial speed control signal, auto control means for varyingthe speed control signal generating means to increase the speed of saidvariable speed drive means when the signal BW is less -than the signalBW, and for varying the speed control signal generating means todecrease the speed of said variable speed drive means when thesignal BWis greater than the signal BW, in proportion to the magnitude of thedeviation of BW, from BW,

3. The system set forth in claim 2 wherein the means for generating thesignals BW and BW are cross web scanning basis weight gauges and thesignals BW and BW are instantaneous signals corresponding with thepositions of the gauges with respect to the web.

4. The system set forth in claim 3 wherein said basis weight gauges arebeta ray gauges.

5. The system set forth in claim 3 wherein said means for comparing thesignal BW with the signal BW, is a profile averaging computer whichproduces an average value of BW over a predetermined time period andincludes a comparing circuit by which the average value of signal BW iscompared with the signal BW,, and wherein said means for comparing BWwith BW, is likewise a profile averaging computer which produces anaverage value of BW, over a predetermined time period and includes acomparing circuit by which the average value of signal BW is comparedwith the signal Bwt.

6. The system set forth in claim wherein said means for generating saidmoisture signal D and speed control signal generating means are motoroperated potentiometers.

7, A machine for heat setting a travelling web of textile fabric, saidmachine including means providing a heated environment through which thetextile web travels for heat setting the fabric, said heat setting meanshaving an entry side and an exit side. tentering means extending throughsaid heat setting means for carrying the web through said heat settingmeans. obtaining a uniform standard fabric width at the exit'side of theheat setting means, and for regulating longitudinal shrinkage of thefabric, overfeed means on the entry side of said heat setting means formoving the fabric web from a source of supply onto the tentering meansat a speed greater than the speed of said tentering means, means forwinding the fabric web after it has passed through said heat settingmeans, means for varying the speed of said overfeed means, a system forcontrolling the final basis weight of said textile web comprising meansproviding a target signal indicative of a desired final basis weighton'the exit side of said heat setting means, means providing a feedbacksignal indicative of the actual final basis weight, means comparing saiddesired final basis weight target signal with said feedback signal toprovide a first error signal represent- .ing any difference between saidsignals, means providing a signal representing the percent moisture inthe fabric on the entry side of said heat setting means, meansresponsive to said first error signal for automatically varying saidpercent moisture signal in proportion to the magnitude of said firsterror signal, means providing a predicted final basis weight signalderived from the basis weight of the fabric coming from supply, thespeed of said fabric coming from supply, the width of the fabric comingfrom supply, the speed of the fabric on the exit side of the heatsetting means, the standard exit width of said fabric, and said percentmoisture signal, means for comparing said predicted basis weight,

signal with said target signal to provide a second error signalrepresenting-any difference between said pre-.

dicted and target signals, and means responsive to said second errorsignal to provide a control signal to vary the speed of said overfeedspeed varying means in order to control the amount of fabric overfeedonto the fabric.

1. A method of improving the uniformity of the basis weight of atravelling web of textile fabric at the exit side of fabric heat settingapparatus which includes a source of wet fabric supply, means for heatsetting the fabric, tentering means for obtaining a uniform standardwidth of the fabric at the exit side of said heat setting means and forregulating the longitudinal shrinkage of the fabric by said heat settingmeans, overfeed means for moving said fabric web from the source ofsupply onto said tentering means, means for winding up said fabric webafter it has passed through said heat setting means and means, forvarying the speed of said overfeed means, comprising the steps ofgenerating a signal BW1 indicative of the measured basis weight of thefabric on the entry side of said heat setting means, generating a signalW1 indicative of the measured width of the fabric on the entry side ofsaid heat setting means, generating a signal S1 indicative of themeasured speed of the web on the supply side of said tentering means,generating a signal S3 indicative of the measured speed of the web onthe exit side of said heat setting means, generating a signal BW2indicative of the measured basis weight of said fabric on the exit sideof said heat setting means, generating a signal BWt indicative of apredetermined target basis weight for the web on the exit side of theheat setting means, comparing the signal BW2 with the signal BWt andproducing an error signal BW2-BWt which corresponds with the deviationof the signal BW2 from BWt, initially setting a signal D1 indicative ofan estimated percent moisture content of the web on the entry side ofthe heat setting means, and thereafter automatically increasing thesignal D1 to indicate an increased percentage moisture when BW2 isgreater than the BWt and decreasing the signal D1 to indicate adecreased Percentage moisture when BW2 is less than BWt in proportion tothe magnitude of deviation of BW2 from BWt, generating a signal BWcindicative of a calculated exit basis weight according to the formula:BWc (BW1/(1 + D1)).(W1/Ws).(S1/S3) wherein BWc, BW1, W1, S1, S3 and D1respectively represent previous indicated signals and Ws represents apreset signal indicative of a selected standard width for said fabric atthe exit side of the heat setting means, comparing the signal BWc withthe signal BWt and generating an error signal BWc-BWt which correspondswith the deviation of BWc from BWt and increasing the speed of theoverfeed means when the signal BWc is less than the signal BWt anddecreasing the speed of the overfeed means when the signal BWc isgreater than the signal BWt.
 2. A system for improving the uniformity ofthe basis weight of a travelling web of knit fabric on the exit side offabric heat setting apparatus which apparatus includes a web fabricsupply source, means for heat setting the fabric, tentering means forobtaining a uniform standard width of the fabric at the exit side ofsaid heat setting means and for regulating the longitudinal shrinkage ofthe fabric by said heat setting means, overfeed means for moving saidfabric web from the source of supply onto said tentering means, meansfor winding up said fabric web after it has passed through said heatsetting means, and variable speed drive means for said overfeed means,comprising means for generating a signal BW1 indicative of the measuredbasis weight of the fabric on the entry side of said heat setting means,means for generating a signal W1 indicative of the measured width of thefabric on the entry side of said heat setting means, means forgenerating a signal S1 indicative of the measured speed of the web onthe supply side of said tentering means, means for generating a signalS3 indicative of the measured speed of the web on the exit side of saidheat setting means, means for generating a signal BW2 indicative of themeasured basis weight of said fabric on the exit side of said heatsetting means, means for generating a signal BWt indicative of apredetermined target basis weight for the web on the exit side of theheat setting means, means for comparing the signal BW2 with the signalBWt and producing an error signal BW2-BWt which corresponds with thedeviation of the signal BW2 from BWt, variable means for generating asignal D1 representing percent moisture content of the web on the entryside of the heat setting means including means for manually setting saidmoisture signal generating means to an initial signal magnitude meansresponsive to the error signal BWc-BWt for automatically increasing thesignal D1 to indicate an increased percent moisture when BW2 is greaterthan the BWt and for decreasing the signal D1 to indicate a decreasedpercentage moisture when BW2 is less than BWt in proportion to themagnitude of deviation of BW2 from BWt, computer means for generating asignal BWc indicative of a calculated exit basis weight according to theformula: BWc (BW1/(1 + D1)).(W1/Ws).(S1/S3) wherein BWc, BW1, W1, S1, S3and D1 respectively represent signals previously defined and Wsrepresents a preset signal indicative of a selected standard width forsaid fabric at the exit side of the heat setting means, means forcomparing the signal BWc with the signal BWt and for generating an errorsignal BWc-BWt which corresponds with the deviation of BWc from BWt,means for generating a speed control signal which controls the speed ofsaid variable speed drive including means for manually setting aninitial speed control signal, auto control means for varying the speedcontrol signal generating means to increase the speed of said variablespeed drive means when the signal BWc is less than the signal BWt andfor varying the speed control signal generating means to decrease thespeed of said variable speed drive means when the signal BWc is greaterthan the signal BWt in proportion to the magnitude of the deviation ofBWc from BWt.
 3. The system set forth in claim 2 wherein the means forgenerating the signals BW1 and BW2 are cross web scanning basis weightgauges and the signals BW1 and BW2 are instantaneous signalscorresponding with the positions of the gauges with respect to the web.4. The system set forth in claim 3 wherein said basis weight gauges arebeta ray gauges.
 5. The system set forth in claim 3 wherein said meansfor comparing the signal BW2 with the signal BWt is a profile averagingcomputer which produces an average value of BW2 over a predeterminedtime period and includes a comparing circuit by which the average valueof signal BW2 is compared with the signal BWt, and wherein said meansfor comparing BWc with BWt is likewise a profile averaging computerwhich produces an average value of BWc over a predetermined time periodand includes a comparing circuit by which the average value of signalBWc is compared with the signal BWt.
 6. The system set forth in claim 5wherein said means for generating said moisture signal D1 and speedcontrol signal generating means are motor operated potentiometers.
 7. Amachine for heat setting a travelling web of textile fabric, saidmachine including means providing a heated environment through which thetextile web travels for heat setting the fabric, said heat setting meanshaving an entry side and an exit side, tentering means extending throughsaid heat setting means for carrying the web through said heat settingmeans, obtaining a uniform standard fabric width at the exit side of theheat setting means, and for regulating longitudinal shrinkage of thefabric, overfeed means on the entry side of said heat setting means formoving the fabric web from a source of supply onto the tentering meansat a speed greater than the speed of said tentering means, means forwinding the fabric web after it has passed through said heat settingmeans, means for varying the speed of said overfeed means, a system forcontrolling the final basis weight of said textile web comprising meansproviding a target signal indicative of a desired final basis weight onthe exit side of said heat setting means, means providing a feedbacksignal indicative of the actual final basis weight, means comparing saiddesired final basis weight target signal with said feedback signal toprovide a first error signal representing any difference between saidsignals, means providing a signal representing the percent moisture inthe fabric on the entry side of said heat setting means, meansresponsive to said first error signal for automatically varying saidpercent moisture signal in proportion to the magnitude of said firsterror signal, means providing a predicted final basis weight signalderived from the basis weight of the fabric coming from supply, thespeed of said fabric coming from supply, the width of the fabric comingfrom supply, the speed of the fabric on the exit side of the heatsetting means, the standard exit width of said fabric, and said percentmoisture signal, means for comparing said predicted basis weight signalwith said target signal to provide a second error signal representingany difference between said predicted and target signals, and meansresponsive to said second error signal to provide a control signal tovary the speed of said overfeed speed varying means in order to controlthe amount of fabric overfeed onto said tentering means and thus tocontrol the amount of fabric shrinkage which effects the final basisweight of the fabric.